Involucrin is an important precursor of the cornified envelope and the only one that has been visualized using biophysical techniques (Yaffe Beegan and Eckert, J. Biol. Chem. 1992). During terminal differentiation it acts as an amine donor and is crosslinked to various amine acceptors in a trans-glutaminase catalyzed crosslinking reaction. Because of the high content of glutamine residues spaced at equal intervals along its length, its elongated rod-like alpha-helical structure and its abundance, involucrin is likely to be the major intramolecular crossbridging molecule of the cornified envelope. It is likely that a single involucrin molecule can crosslink many other molecules in the envelop. Expression of involucrin is confined to external surface epithelial cells. It is specifically expressed suprabasally in these tissues and is not present in the basal layer. In addition, it is tightly regulated during development with expression beginning in the periderm and in the epidermis proper at the end of the first trimester. Several interesting abnormalities of involucrin expression are observed in epidermal diseases including squamous cell carcinoma. To ultimately understand the process of normal and abnormal epidermal differentiation, it is essential to understand the molecular mechanisms responsible for regulation of genes specifically expressed in epidermis. At present, no knowledge is available regarding the molecular events responsible for the activation of involucrin gene expression during differentiation and development. The major aim of the present proposal is to study these molecular events using a transgenic mouse model. This will provide us with a detailed profile of involucrin expression during epidermal differentiation and fetal development and new knowledge concerning the molecular events responsible for regulation of involucrin expression. It will also provide other benefits for future experimentation not outlined in this proposal, including a well characterized promoter for use in targeting genes to the epidermis.